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Optical Path - Practice Questions & MCQ

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

Quick Facts

  • 4 Questions around this concept.

Solve by difficulty

PQR is a right angled prism with other angles as 60^{\circ}  and 30^{\circ} . Refractive index of prism is 1.5. PQ has a thin layer of liquid. Light falls normally on the face PR. For total internal reflection, maximum refractive index of liquid is

White light may be considered to be a mixture of waves  \lambda ranging between 3900 \mathrm{~A}^{0} and 7800 \mathrm{~A}^{0}. An oil film of thickness 10,000 A^{0} is examined normally by a reflected light. If \mu=1.4, then the film appears bright for

Concepts Covered - 1

Optical path

Optical path-

It is defined as the distance travelled by light in a vacuum, in the same time in which it travels a
given path length in a medium.

Let light cover distance t in the medium having a refractive index as \mu in Time T.

So  T=\frac{t}{v} where v=speed of light in the medium

and \mu=\frac{c}{v}  where c=speed of light in the vacuum.

So T=\frac{t\mu }{c}

So in the same time T distance covered by light in a vacuum is l= cT=c*\frac{\mu t}{c}=\mu t

So the relation between geometrical path (t) and optical path (l) is given as l= \mu t

  • For two medium in contact as shown in the below figure

the optical path is equal to \mu_{1} x_{1}+\mu_{2} x_{2}

  • Change in the optical path in a transparent slab

Consider the following two cases

Case I-  A light cover distance l=AB

So the optical path in this case is L_1=l

Case II- Now a slab of thickness t is placed between A and B

So distance travells in slab=t

and distance travells in air=l-t

So the optical path in this case is  L_2=(l-t)+\mu t

Now change in the optical path = \Delta x=L_2-L_1= [(l-t)+\mu t]-[l]=t(\mu -1)

I.e due to insertion of the slab the optical path is increased by \Delta x =t(\mu -1)


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Optical path

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